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Presentation Transcript

Slide1:

Contents :

Contents 2D Drawing Principles:
Tolerances
ANSI/ISO Tolerance Designation
ANSI/ISO Classification of Limits and Fits
Surface Properties
Economics of Tolerances/Surface properties Attention to Detail
The engineering drawing is the specification for the component or assembly and is an important contractual document with many legal implications, every line and every comment is important.

Part and Assembly Drawings:

Part and Assembly Drawings
Assembly Drawings:
Assembly drawings are used to show the position and functional relationship of parts in an assembly, also via multiview orthographic projections.
Generally they have no dimensions on them.
Parts are 'balloon' identified and referenced to either detail drawing numbers or catalog numbers, via a Bill of Materials (BOM) Part Drawings:
Detail drawings completely describe a single part with multiview orthographic projections.
Should provide all the information necessary to economically manufacture a high quality part.

Orthographic Views:

The Glass Box Concept :

The Glass Box Concept

Slide6:

The glass box concept theorizes that an object is suspended inside a six-sided glass cube (notice the use of hidden lines on the glass box, depicting lines that would not be visible from the given perspective).

Slide7:

As the object is viewed from a specific orientation (perpendicular to one of the sides of the cube) visual rays project from the object to the projection plane. These projectors are always parallel to each other.

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The object’s image is formed on the projection plane by the pierce points of the visual rays.

Slide9:

The process is repeated to construct the right side view on the profile plane

Slide10:

Similarly, the top view is projected to the horizontal plane

Slide11:

For many three-dimensional objects, two to three orthographic views are sufficient to describe their geometry.

Slide12:

The box can be unfolded to show the multiple views in a single x-y plane

Slide13:

FRONT TOP RIGHT SIDE Because the observation point is located at infinity, the integrity of feature size and location are maintained, and the views are oriented orthogonally in relationship to each other.

Slide14:

Notice that the projectors or extension lines, are perpendicular to the folding lines of the glass box. (Fold lines and extension lines are drawn very lightly, when used, and are not part of the finished drawing.)

Dimensional Data can then be added to the drawing:

Dimensional Data can then be added to the drawing There are 3 distinct line weights to be aware of:
object lines are thick (approximately .030-.040” thick),
hidden lines are a medium thickness (.015-.020”), and
extension, dimension, and center lines are thin (.007-.010”).

Slide17:

Complete the 3 view drawing (without dimensions for now). Begin by projecting all of the known information between the views.

Slide18:

Begin by projecting all of the known information between the views.

Slide19:

Heavy-up all of the object lines that depict visible object lines, and show surfaces that would not be visible in the specific orientation, using dashed/hidden lines.

Slide20:

Complete the right side view by projecting all of the relevant lines and points using a 45 degree miter line. Clean up the drawing.

Slide21:

Remove the final construction lines to see the finished drawing

Section Views:

Section Views Section views are used to clarify internal detail and to avoid dimensioning to hidden lines
The are established by referencing a cutting plane
Cutting planes depict the exact location on the part from which the section view will be projected, and should have associated arrowheads, indicating the direction from which the section view will be observed.
Cutting planes are constructed as an integral feature of the parent view, and cutting plane arrowheads always indicate the direction for the observer’s line of sight. A A SECTION A - A

Projected Section Views:

A A SECTION A – A
ROTATED 30º CLOCKWISE Projected Section Views

Cutting Plane:

Alpha Characters A - A, B - B, C – C*, etc., are used to designate the required section view. The characters are placed near the arrowheads and as a subtitle of the view. There is no “standard” for the location of the section designators, other than near the cutting plane arrowheads—as the examples below illustrate.
When the alphabet has been exhausted, use double characters AA - AA, BB - BB, CC – CC*, etc.
*Section Designators should NOT include the alpha characters I, O, or Q. A A SECTION A - A Cutting Plane Subtitle of actual view Cutting plane on reference view

Crosshatching Section Views:

Crosshatching Section Views Crosshatching, is a repeating graphic pattern which is applied throughout all areas of the part that would be in contact with the cutting plane. Thus, the hole is not crosshatched.
The recommended angle for the standard crosshatch pattern is 45, 30, or 60 degrees with horizontal. Similarly, crosshatch lines should be neither parallel nor perpendicular to the outline of the feature in section—if avoidable (see the examples below). Good Practice Poor Practice Poor Practice

Slide29:

The general purpose cross hatch is used in most individual detail component drawings and in assembly applications where no confusion will result.
Each of the assembled components are depicted with a different crosshatch angle to assist in part differentiation.
Specific crosshatch symbols are sometimes used to represent each different material type. Cross Hatch Standards

Slide30:

Half Sections:

Half Sections Half section views are the result of cutting planes being positioned on parts in such a manner that only half of the resulting view or projection is shown in section.
Half sections are generally used on objects of symmetry, individual cylindrical parts, or assemblies of parts.

Half Sections:

Half Sections Shown without section:
Difficult to dimension without using hidden lines
Internal features – not as clear

Offset Sections:

Offset Sections Offset sections allow us to provide greater breadth of detail with fewer section views. All of the features are aligned with the cutting plane. SECTION D - D

Coordinate Dimensioning and Tolerancing:

Coordinate Dimensioning and Tolerancing The collective process of modeling, defining and describing geometric sizes and feature relationships, and providing all of the required technical information necessary to produce and inspect the part is called dimensioning and tolerancing.
The current National Standard for dimensioning and tolerancing in the United States is ASME Y14.5M - 1994.
DRAWN IN ACCORDANCE WITH ASME Y14.5M - 1994
REMOVE ALL BURRS AND SHARP EDGES
ALL FILLETS AND ROUNDS R .06 UNLESS OTHERWISE SPECIFIED

Drawing Notes:

Drawing Notes DRAWN IN ACCORDANCE WITH ASME Y14.5M - 1994
REMOVE ALL BURRS AND SHARP EDGES
ALL FILLETS AND ROUNDS R .06 UNLESS OTHERWISE SPECIFIED Notes should be concise and specific. They should use appropriate technical language, and be complete and accurate in every detail. They should be authored in such a way as to have only one possible interpretation.
General Notes Local Notes 4X 8.20 M10 X 1.25
82º CSK 10
1.5 X 45º CHAM

Arrowheads:

Arrowheads Arrowheads are used as terminators on dimension lines. The points of the arrowheads on leader lines and dimension lines must make contact with the feature object line or extension lines which represent the feature being dimensioned. The standard size ratio for all arrowheads on mechanical drawings is 3:1 (length to width). 1st 2nd 3rd 4th Of the four different arrowhead types that are authorized by the national standard, ASME Y14.2M – 1994, a filled arrowhead is the highest preference.

Slide38:

Dimensions should be placed outside the actual part outline. Dimensions should not be placed within the part boundaries unless greater clarity would result. There should be a
visible gap (~1.5 mm)
between the object lines
and the beginning of
each extension line. Extension lines overlap dimension lines (beyond the point of the arrowheads) by a distance of roughly 2-3mm
1.75 1.06 Dimension Lines and Extension Lines

Slide39:

Arrows in / dimension in Arrows out / dimension in Arrows in / dimension out Arrows out / dimension out 2.562 1.250 .750 .500 Placement of Linear Dimensions Order of Preference When there is not enough room between the extension lines to accommodate either the dimension value or the dimension lines they can be placed outside the extension lines as shown in the fourth example (use Flip Arrows in ProE).

Slide40:

Reference Dimension Symbol (X.XXX) Reference dimensions are used on drawings to provide support information only.
They are values that have been derived from other dimensions and therefore should not be used for calculation, production or inspection of parts.
The use of reference dimensions on drawings should be minimized. EXAMPLE 2.250 1.000 (.750) .500 1.250 .500 (.750) .500 Reference Dimensions

Slide43:

Slide44:

Whenever it is practical to do so, external diameters are dimensioned in rectangular (or longitudinal) views. Cylindrical holes, slotted holes, and cutouts that are irregular in shape would normally be dimensioned in views where their true geometric shape is shown. Diameter Dimensions
Shafts and Holes

Slide47:

“Times” and “By” Symbol: X:

“Times” and “By” Symbol: X The X symbol can also be used to indicate the word “by”. For instance, when a slot that has a given width by a specified length, or a chamfer that has equal sides (.12 X .12).
When used to imply the word ‘by’, a space must precede and follow the X symbol.
If the same feature is repeated on the drawing (such as 8 holes of the same diameter and in a specified pattern), the number of times the instruction applies is called out using the symbol X. .12 X 45º
CHAMFER .375
.562 X 82º CSK

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ASME/ANSI Hole Depth Symbol:

Depth or Deep Symbol* * This symbol is currently not used in the ISO standard. It has been proposed. .375
.625 EXAMPLE .375 .625 OR ASME/ANSI Hole Depth Symbol Features such as blind holes and counterbores, must have a depth called out to fully describe their geometry.

ASME/ANSI Countersink Symbol:

Countersink Symbol* ASME/ANSI Countersink Symbol The symbol denotes a requirement for countersunk holes used to recess flathead screws. The height of the symbol is equal to the letter height on the drawing, and the included angle is drawn at 90º. Note that this symbol is not used in the ISO (international) standard. * This symbol is currently not used in the ISO standard. It has been proposed. EXAMPLE

ASME/ANSI Counterbore Symbol:

Counterbore Symbol* This symbol denotes counterbored holes used to recess machine screw heads. * This symbol is currently not used in the ISO standard. It has been proposed. EXAMPLE .562 .312 .375 OR ASME/ANSI Counterbore Symbol

Slide56:

Slide57:

Tolerancesimportant to interchangeability and provision for replacement parts :

Tolerances important to interchangeability and provision for replacement parts It is impossible to make parts to an exact size. The tolerance, or accuracy required, will depend on the function of the part and the particular feature being dimensioned. Therefore, the range of permissible size, or tolerance, must be specified for all dimensions on a drawing, by the designer/draftsperson.
Nominal Size: is the size used for general identification, not the exact size.
Actual Size: is the measured dimension. A shaft of nominal diameter 10 mm may be measured to be an actual size of 9.975 mm.
General Tolerances:
In ISO metric, general tolerances are specified in a note, usually in the title block, typically of the form: "General tolerances ±.25 unless otherwise stated".
In English Units , the decimal place indicates the general tolerance given in the title block notes, typically:
Fractions = ±1/16, .X = ±.03, .XX = ±.01, .XXX = ±.005, .XXXX = ±0.0005,
Note: Fractions and this type of general tolerancing is not permissible in ISO metric standards.

Slide59:

Specific Tolerances indicate a special situation that cannot be covered by the general tolerance.
Specific tolerances are placed on the drawing with the dimension and have traditionally been expressed in a number of ways: Specific Tolerances 40 +0.05
- 0.03 40.01 +0.04 40.05
39.97 Bilateral Tolerance Unilateral Tolerance Limit Dimensions Limits are the maximum and minimum sizes permitted by the the tolerance. All of the above methods show that the dimension has:
a Lower Limit = 39.97 mm
an Upper Limit = 40.05 mm
a Tolerance = 0.08 mm
Manufacturing must ensure that the dimensions are kept within the limits specified. Design must not over specify as tolerances have an exponential affect on cost. -

Limits and Fits:

Limits and Fits 1. Clearance Fits
The largest permitted shaft diameter is smaller than the diameter of the smallest hole

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2. Interference Fits
The minimum permitted diameter of the shaft is larger than the maximum diameter of the hole
3. Transition Fits
The diameter of the largest allowable hole is greater than that of the smallest shaft, but the smallest hole is smaller than the largest shaft

ISO Tolerance Designation:

ISO Tolerance Designation The ISO system provides for:
21 types of holes (standard tolerances) designated by uppercase letters A, B, C, D, E....etc. and
21 types of shafts designated by the lower case letters a, b, c, d, e...etc.
These letters define the position of the tolerance zone relative to the nominal size. To each of these types of hole or shaft are applied 16 grades of tolerance, designated by numbers IT1 to IT16 - the "Fundamental Tolerances":
ITn = (0.45 x 3 D +0.001 D) Pn
where D is the mean of the range of diameters and Pn is the progression:1, 1.6, 2.5, 4.0, 6.0, 10, 16, 25......etc. which makes each tolerance grade approximately 60% of its predecessor.

For Example::

For Example: Experience has shown that the dimensional accuracy of manufactured parts is approximately proportional to the cube root of the size of the part.
Example:
A hole is specified as: 30 H7
The H class of holes has limits of . i.e. all tolerances start at the nominal size and go positive by the amount designated by the IT number.
IT7 for diameters ranging 30- 50 mm:
+ x
+ 0 Tolerance for IT7 = (0.45 x 3 40 +0.001x 40) 16 = 0.025 mm Written on a drawing as 30 H7

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Selection of Fits and theISO Hole Basis system:

Selection of Fits and the ISO Hole Basis system From the above it will be realized that there are a very large number of combinations of hole deviation and tolerance with shaft deviation and tolerance. However, a given manufacturing organization will require a number of different types of fit ranging from tight drive fits to light running fits for bearings etc. Such a series of fits may be obtained using one of two standard systems:
The Shaft Basis System:
For a given nominal size a series of fits is arranged for a given nominal size using a standard shaft and varying the limits on the hole.
The Hole Basis System:
For a given nominal size, the limits on the hole are kept constant, and a series of fits are obtained by only varying the limits on the shaft.
The HOLE SYSTEM is commonly used because holes are more difficult to produce to a given size and are more difficult to inspect. The H series (lower limit at nominal, 0.00) is typically used and standard tooling (e.g. H7 reamers) and gauges are common for this standard.

ISO Standard "Hole Basis" Clearance Fits:

ISO Standard "Hole Basis" Clearance Fits Type of Fit Hole Shaft Loose Running Fits . Suitable for loose pulleys and the looser fastener fits where freedom of assembly is of prime importance H11 c11 Free Running Fit. Where accuracy is not essential, but good for large temperature variation, high running speeds, heavy journal pressures H9 d10 Close Running Fit. Suitable for lubricated bearing, greater accuracy, accurate location, where no substantial temperature difference is encountered. H8 f7 Sliding Fits . Suitable for precision location fits. Shafts are expensive to manufacture since the clearances are small and they are not recommended for running fits except in precision equipment where the shaft loadings are very light. H7 g6 Locational Clearance Fits . Provides snug fit for locating stationary parts; but can be freely assembled and disassembled. H7 h6